1. Field of the Invention
This invention relates to a miniaturized electric contact assembly for a microswitch including a mating contact wherein the term "contact assembly" used throughout the specification means an assembly having a contact joined with a base material and wherein the contact as joined with the base material is brought into contact with the mating contact.
2. Description of the Prior Art
Conventional contact assemblies are produced by or by molding a contact material into a rivet shape and calking the rivet-shaped contact material into a hole in a base material. The former contact assemblies pose problems in that the area of connection between the contact material and the base material, i.e. the section area of the welded portion, is small and in that a defective weld sometimes occurs. The latter contact assemblies pose a problem in terms of efficiency because the contact materials molded into a rivet shape are inserted into the calked on the base material one by one.
The inventor has previously proposed a method for the manufacture of contact assemblies by pressing, which is disclosed in Japanese Patent Publication No. SHO 55(1980)-24365. This method uses a continuous die press capable of simultaneously carrying out a number of processes and comprises punching a hole in a web sheet of base material, raising the base material surrounding the hole, laterally cutting a slice from a round rod of contact material being vertically fed down to a position obliquely upward of the hole, vertically inserting the slice of contact material into the hole and calking the contact material into the hole, whereafter the base material is cut to produce a miniaturized contact assembly suitable for use in a microswitch. The inventor has also proposed a method for the mass production of contact assemblies having rectangular contacts, which comprises horizontally feeding a rectangular material for contacts to a continuous die press, shearing the end thereof by punching and, at the same time, successively inserting the sheared materials into the punched rectangular holes, calking the inserted materials and cutting off the individual contact assemblies (U.S. Pat. No. 4,259,557).
The contact assemblies made by calking with a press overcome the problems encountered in the aforementioned contact assemblies made by projection welding and by calking of a rivet-shaped contact material, and have earned a good reputation as high-performance contact assemblies having excellent conductivity and a heat transfer property between the contact and the base material.
In manufacturing the aforementioned contact assemblies by projection welding or by calking of a rivet-shaped contact material, it has heretofore been impossible from the point of manufacture to make the contacts very small. Although it is possible to make the contacts smaller in accordance with the methods disclosed in the aforementioned Japanese Publication and U.S. Patent, contacts of such a small size increase in temperature due to their electric resistance and the instantaneous electric arc resulting from repeated use thereof relative to mating contacts. Since they have small thermal capacity and their surface areas through which heat is diffused onto the base material or in the atmosphere are also small, the temperature thereof becomes larger and larger, with the result that there arises a possibility of the smaller contacts being fused. For these reasons, it has been known that contacts have to have a size large enough so that the surface area thereof can be more than ten times the predetermined actual contact area.
On the other hand, owing to the development of miniaturized and simplified control devices, small switches of high capacity which allow a main current to flow without use of a relay have come into demand. To meet this demand, ultra-miniaturized switches of the size of beams, which exhibit a high capacity on the order of AC 125 V, 7 A, for example, have recently been developed and are now commercially available on the market. In ordinary switches, the contact is made of silver and the base material is generally made of brass, from the standpoints of conductivity, strength and manufacturing cost. However, in the aforementioned small switches of high capacity, both the contact and the base material are made of silver and, therefore, the switches are very expensive as compared with conventional switches and have come to be utilized in space devices and for military and other special purposes.